Conventionally, in an electronic apparatus such as a communication device and a server device, there is provided a power supply device that supplies power to an IC or the like that executes various kinds of processing. Such power supply device is required of supplying stable power consistently, and in particular, required of adjusting an output voltage that is outputted to an IC or the like to be constant.
FIG. 1 schematically illustrates a structure of a power supply device that supplies power to an electronic apparatus.
A power supply device 10 illustrated in FIG. 1 is a power supply device employing an analog control method in which an output voltage to an IC or the like is controlled with the use of an analog component such as an amplifier and a comparator.
The power supply device 10 includes a voltage detection circuit 11, an error amplifier 12, a compensation circuit 13, a reference oscillator 14, a comparator 15, a switch element 16, a smoothing filter 17 and so on.
Firstly, in the voltage detection circuit 11, a power output voltage Vout that is currently outputted from the power supply device 10 to an IC or the like is detected, and the detected output voltage Vout is transmitted to the error amplifier 12. In the error amplifier 12, a difference between the output voltage Vout and a reference voltage V0 is amplified and outputted. In the compensation circuit 13, an amplified voltage Vg that is outputted from the error amplifier 12 is adjusted to a value appropriate to the sensitivity of the comparator 15.
In the reference oscillator 14, a voltage signal Vp of sawtooth waveform is outputted at a given frequency. In the comparator 15, the voltage signal Vp of sawtooth waveform outputted from the reference oscillator 14 is compared with the amplified voltage Vg that has been adjusted in the compensation circuit 13, and a control signal that becomes “ON” while the voltage signal Vp of sawtooth waveform is smaller than the amplified voltage Vg, and becomes “OFF” at all other times is transmitted to the switch element 16.
In the switch element 16, since “ON-OFF” is thus controlled by the control signal transmitted from the comparator 15, a pulse width of the input voltage Vin that has been inputted to the power supply device 10 is adjusted, and a smoothing operation is executed in the smoothing filter 17. As a consequence, the output voltage Vout of which voltage value has been adjusted is outputted from the power supply device 10 to an electronic apparatus. For example, if the output voltage Vout detected in the voltage detection circuit 11 drops, an error between the output voltage Vout and the reference voltage V0 which is calculated in the error amplifier 12 becomes large. As a consequence, the voltage signal Vp of sawtooth waveform becomes smaller than the amplified voltage Vg, causing “ON” duration of the control signal outputted from the comparator 15 longer, so that the pulse width of the input voltage Vin is adjusted to be longer and the output voltage Vout is raised.
In the power supply device 10, the output voltage that is outputted to a processing section is controlled to be constant as described above.
Here, in an electronic apparatus, various kinds of components, an IC and the like which are included in the electronic apparatus is supplied with power to operate. In these components, the IC and the like, a power consumption changes in accordance with an amount of load in processing shared by each of the components, the IC and the like. If such individual fluctuation of load is moderate, it is possible to supply required power consistently by absorbing the fluctuation of load in each component and thus maintaining a voltage to be applied to the components and the IC or the like to be constant. However, in a communication device or a server device among the electronic apparatuses, there is a case in which a load in the IC or the like that executes communication processing abruptly fluctuates in synchronization with a state of communications traffic, which makes it difficult to absorb abrupt fluctuations of load in such a local place under an overall control by a single power supply device.
For this reason, there is proposed a technique that absorbs local fluctuations of load individually and maintains necessary power supply independently by providing plural power supply devices in such a manner that at least one power supply device is disposed near the various kinds of components, the IC and the like included in the electronic apparatus, and by individually controlling a voltage to be applied to the various kinds of components, the IC and the like (see U.S. Pat. No. 6,646,425, for example).
However, even if the voltage to be applied to the various kinds of components and the IC or the like is controlled individually by the technique disclosed in the U.S. Pat. No. 6,646,425, in a case where fluctuations of load in a component that adjoins a component targeted for controlling by a power supply device are too large, there often occurs a problem that the power supply device may not be able to maintain proper power supply to the control target, by being affected by the fluctuations of load in other component that is not targeted for controlling.